Many medical benefits could be realized if the immune system could be trained to respond to antigens in a desired manner, such as by developing tolerance to (e.g., for an allergic antigen or auto-antigen), or by learning to reject (e.g., for a disease-associated antigen) the antigen. The body can react to a wide variety of antigens, whether exogenous antigens (e.g., allergens, infectious agent antigens, etc) or endogenous antigens (e.g., auto-antigens, certain disease-associate antigens, etc). Diverse approaches have been applied in order to meet this challenge, including systemic drug treatments, injection of antigens, antibody therapies, etc. However, there remains a need for improved approaches.